power supply fail

Discussion in 'General Electronics Chat' started by FroceMaster, Mar 19, 2015.

  1. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi. Have this powersup
    i get apr. 300v dc at the 2 transistors D13009K but i dont get any outputs.
    Can it just be that these are fried ??
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    Probably not those but something further down the line maybe?
    Chinese origin is a clue, they are renown for not being very rugged and early failure.
    Max.
     
    Lundwall_Paul likes this.
  3. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    It's possible but I wouldn't bet on it. They tend to fail more spectacularly.

    My bet would be bad capacitors. If you're out of things to try, replace all the electrolytic capacitors. It'll only cost a few bucks.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,986
    3,729
    @FroceMaster

    The following two issues may be from a poor photo but check them to be sure.

    - Check the big cap near the transistors. It looks like that one had some gas/vapor escape at one time. If so, it is bad.

    - Also, look at the large yellow-taped transformer. It looks like the yellow tape got all puckered from overheating.

    - Also look at the heat sink of Q1. It looks bent and out of place and may be touching Pin 1, which it shouldn't be touching.
     
    Roderick Young likes this.
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    whats the 16 pin chip number, maybe a TL494 ...
     
  6. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    No power to that chip. Cant remember the number right now. But it's some PWM chip
     
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    can you take pictures of the chip and track side of the pcb, maybe there is a fusible resistor, looks like an Atx psu.
     
  8. Evil Lurker

    Member

    Aug 25, 2011
    117
    23
    I had to let out a chuckle when I read the manufacturer of those caps... "Rubicong" an obvious rip-off of the respected Japanese manufacturer "Rubycon". This is the first time I have ever heard of this outfit... I actually have a few "Rulycon" capacitors in my collection. Sadly I opened one up only to find it was an actual capacitor, not a smaller capacitor shoved into the can of a larger cap and mislabeled.

    Anyways, every single one of those caps should be considered suspect and replaced on sight, at least that is how I would deal with. And check out the issue with the primary switching transistors as well, that first pin does look awfully misaligned. I think the transformer is probably ok, looks like sticky foam residue.
     
  9. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    Apologies in advance for asking something so simple, but is there high voltage DC present on the rectified line supply? It couldn't just be a blown fuse could it?
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    op says there is 300V DC on the caps, pwm chip has no dc maybe a fusible resistor...
     
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